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Total marrow irradiation (TMI) and total body Irradiation (TBI) delivered on the linac couch are limited by the couch travel range of linacs, which forces to split the treatment delivery into two plans with opposite orientations. A specific field junction is thus needed to obtain a robust target coverage in the overlap region of the two plans. An automatic tool (AT) for (a) field junction creation and (b) lower-extremities plan optimization was developed in a centre with a dedicated team. Despite the creation and local use of scripts is increasing, it is not clear whether they are easily transferable across Institutions (Inst.), as different clinical practices and the limited experience in scripting constitute a barrier in their widespread adoption. The purpose of this study is to perform a multicentric validation of the AT across 5 centres.

Ten VMAT-TMI patients were selected retrospectively at Inst.1, where the AT was developed for the Eclipse TPS (Varian). The planning of the lower-extremities was performed with the AT and compared with the manual plans by considering target volume parameters (CTV_J-V98%>98%) at the junction region and several dose statistics (D98%, Dmean, and D2%) using Wilcoxon signed-rank test (p<0.05 significant). The automatic tool was shared with 4 international Inst. to perform a multicentric validation in different scenarios: VMAT-TMI, VMAT-TBI, and Tomotherapy-TBI, with dose prescriptions varying from 2 Gy in single fraction to 13 Gy in 9 fractions.

The AT required 60-90 minutes (a+b), while manual planning could take up to 2 working days, depending on the case. All automatic plans achieved clinically acceptable dosimetric results (Table 1). In March 2022 the AT was introduced in clinical practice at Inst.1, allowing to reduce the TMI simulation-to-delivery schedule by 2 days. All Inst. were able to install the AT, but several difficulties were encountered due to different clinical practices and experience between centres. The following results were obtained: (i) since Sept. 2022, Inst.2 with little experience in TMI treatments managed to treat 3 VMAT-TMI patients using the AT (a+b), greatly reducing the planning time and streamlining the TMI planning process; (ii) Inst.3, having no experience with TMI treatments, tested the AT (a) for the upcoming introduction of VMAT-TMI; (iii) Inst. 4 evaluated the AT (a) to streamline VMAT-TBI planning; (iv) Inst.5 tested the AT (a) on a Tomotherapy-TBI patient. The AT’s output and the final plan obtained for a representative case at different Inst. are shown in Figure 1.

The AT can streamline the RT planning process, increasing efficiency and time savings. Multicentric validations should be performed to assess the efficacy and simplify the clinical implementation of automatic tools in centres without dedicated teams. This work was supported by grant GR-2019-12370739.